Optical crown glass



y Wm H. BROEMER ETAL 3,51%,325

QPTICAL CROWN GLASS Filed Aug. 10. 1965 as a0 a5 I/Vl/ENTOR S HEINZBROEMER and NORBERT MEINERT A TTORNE Y.

United States Patent Of 3,510,325 OPTICAL CROWN GLASS Heinz Broemer,Hermannstein, Kreis Wetzlar, and Norbert Meinert, Wetzlar (Lahn),Germany, assignors to Fa. Ernst Leitz G.m.b.H., Wetzlar, Germany FiledAug. 10, 1965, Ser. No. 478,607 Claims priority, application Germany,Sept. 23, 1964, L 48,849 Int. Cl. (1031c 3/08, 3/14 US. Cl. 106-54 4Claims ABSTRACT OF THE DISCLOSURE An optical crown glass may be producedby melting a mixture consisting essentially of 50 to 85% by weight of BSiO and A1 0 9 to 40 weight percent of bivalent oxides and other metaloxides. The following mixture is illustrative: B 0 amounting to 42-46%,SiO at 0-3 weight percent, A1 0 at 916.5 weight percent, the totalconcentration of these oxides in the mixture being from 55 to 62 weightpercent; CaO at 20-25 weight percent, BaO at 0-3 weight percent, ZnOand/or CdO at 0-10 weight percent, the total concentration of bivalentoxides being from 23 to 35 weight percent; and La O at 14-16 weightpercent, Zr0 at 0-10 weight percent, and Ta O at 0-5 weight percent.

This invention relates to improved optical crown glasses manufacturedfrom novel starting mixtures.

DESCRIPTION OF THE PRIOR ART Mass production of high-quality opticalsystems is currently required to meet present day requirements. As aresult, the requirements and standards which must be met by opticalglass have greatly increased. Of particular significance in this respectare the glasses employed in continuous melting processes and thechemical stability thereof. Other standards which the glass must meetinclude the preservation of the optical position, clarity and absence ofcolor, and the moldability of the glasses. However, in previous knownoptical crown glasses having indices of refraction n of approximatelyfrom 1.55 to 1.65 and dispersion values v of approximately from 55 to62, all of these requirements have not been met.

SUMMARY OF THE INVENTION It is the object of this invention to provideoptical crown glasses and mixtures from which they can be formed whichhave the requisite characteristics for use in continuous meltingprocesses, and which have superior chemical stability and resistance,retention of optical position, clarity and absence of color, and moldingcharacteristics.

Starting mixtures for the manufacture of optical crown glasses have nowbeen found which may be melted without difficulties in the continuousprocess and which moreover meet all the requirements enumeratedhereinabove. They are, therefore, of considerable technicalsignificance.

BRIEF DESCRIPTION OF THE DRAWING The three component diagram illustratesthe relative proportions of boric acid, silicic acid and aluminum oxideemployed in the composition. The starting mixtures of the crown glassesaccording to the present invention consist-in an amount from 50 to 85percent by weight-of boric acid, silicic acid and aluminum oxide. Therelative proportions of these constituents, as parts per 100 parts ofthe total of the three, are within the three-component diagram in arange which is delimited by the following points:

A B C D E DESCRIPTION OF THE PREFERRED EMBODIMENTS The starting mixturescontain, moreover, a total of from 9 to 40 percent by weight of theoxides of the bivalent elements calcium, strontium, barium and zinc orcadmium. They should contain specifically:

Percent by weight Calcium oxide (at least) 9-37 Strontium oxide 0-10Barium oxide 0-7 Zinc oxide 0-9 For the purpose of adjusting specificoptical values, these glasses furthermore can contain:

Percent by weight Lanthanum oxide 0-16 Zirconium oxide 0-9 Tantalumoxide 0-4 Percent by weight The sum total of these oxides is 55-62percent by weight.

Percent by weight CaO 20-25 BaO 0-3 ZiO and/0r CdO 0-10 The sum total ofthese oxides is 23-35 percent by weight.

Percent by weight La O 14-16 21 02 0-10 Ta205 An example for carryingout the melt of such glass is set forth hereinbelow.

EXAMPLE 1 The ingredients in the concentrations set forth in Melt No. 3in Table 2 below and having a total weight of approximately 3 kilogramswere well mixed and placed in the respective portions into a platinumcrucible having a temperature of approximately 1200 to 1250 C. and weremelted down. The temperature was thereafter raised to 1300 C., and themelt was purified for approximately 60 minutes with continued stirring.Thereupon, and while still constantly stirring, the temperature wasreduced to 1050 C. within about 15 minutes. Without further stirring,the melt was allowed to cool to 900 C. The melt was poured at thattemperature into steel molds which had ben preheated to 600 C.

The transformation point of the glass was at 583 C., the softening pointthereof was at 632 C. The expansion coefficient was 6.15 10 within thetemperature range of from to C. The optical values were n =1.6451 and v=57.8

The extremely low portion of barium oxide and the approximately 3kilograms, were well mixed and placed relatively high portion ofaluminum oxide contributed in portions into a platinum crucible at atemperature substantially to the chemical stability of these glasses. ofapproximately 1300 C. and were melted down. The The latter alsoexhibited superior molding strength chartemperature was thereafterraised to 1400 C., and the acteristics because of the Al O constituent.melt was purified for approximately 60 minutes with con- One of the mostfrequently employed optical crown tinued stirring. Thereupon, and withcontinued stirring, glasses with the optical values ll l.6l and v :60.0can the tcnlperature wa d d t 12()O C ithi b t be melted from startingmixtures which consist of minutes. Vt ithout further stirring, the meltwas allowed to cool to 950 C. Pouring-01f tool; place at that Percent byweight temperature into steel molds which had been preheated B 0 34-4410, to 600 C. SiO 13-2l The transformation point of the glass was at 587C, M 0 5l0 and the softening point thereof was at 642 C. The expansioncoefficient was 6.6 1O* within the temperature The sum total of theseportions should amount to T2111? Of from 100 10 The Optical Valuesbetween 55 and 75 percent by weight. /1 and 5 In the tables which arebeing set forth hereinbelow, detailed and specific starting mixtures forglasses according to the present invention are indicated. Table 1 showsstarting mixtures whose relative proportions of boric acid, silicic acidand aluminium oxide are within the boundaries of the afore-mentionedrange within the threecomponent diagram. The optical values of. theseglasses, which are obviously influenced by the portion of the Thestarting mixtures further contain Percent by weight Calcium oxide -37Barium oxide 2 05 The sum total of the bivalent oxides should be between25 and percent by weight. Lanthanum oxide may be present in thesebatches in an amount of up to 5 percent other flfole-menllomd Oxides 0fThe and tetray Weight and lithium oxide up to 3 percent by weight.valent elements, are between 1.55 and 1.65 for the index The highportion of vitrifiers and of aluminum oxide of refraction )1 and betweenand 61 for the abbe or makes these glasses well readily moldable.Because of the dispersion value v TABLE 1.1N PERCENT OF WEIGHT PER M511N5. no, Sit): 111 0 21 13 0 $103 A1103 050 1150 Z v.

.2 10.3 55. 0 55. 0 10.0 35. 0 57.0 ..s 10.1 04. 0 70.1 20. 0 5s. 4 p010.1 55.0 52.0 18.0 54.7 .2 8. 3 0 75. 0 10. 0 15. 0 57.4 x 5 5 0 70. 020. 0 10.0 57.0 3 4. 8 04. 1 00. 1 7. 00. 5 .0 4.8 54.1 02.4 30.1 7.550. 0 .0 4.8 04.1 54.0 37.0 7.5 50.7 .0 4.8 04.1 40.8 45.7 7.5 50.7

extremely low barium oxide constituent, they are also very stablechemically. Table 2 indicates starting mixtures which result in the Anexample for carrying out the melt of such a glass formation of highlyrefractive glasses similar to the will be given hereinafter. compositionof the glass described in Example T TABLE 2.IN PERCENT OF WEIGHT PER100% A1303 I21 B003 S103 A1105 (3210 B110 Z110 CdO 22 112190 ZrOg T8205n v.

EXAMPLE 2 Table 3 rndrcates startmg mlxtures Watch result in the heingredients in the concentrations set forth in Melt formation of 'JYOWHglasses Wlth 791MB of @116 glassfifi No. l() of Table 3 below and havinga total Weight of 75 specified in the melt-Examp1e 2.

TABLE 3.1N PERCENT OF EIGHT PER 199% Melt N0. B203 S102 A120 21 B203S102 A1203 C210 B30 Z110 22 L920; L120 D 49. 19. 3 5. 0 64. 3 62. 2 30.0 7. 8 30. 9 59. 7 40. 0 19. 3 l0. 0 69. 3 57. 8 27. 8 14. 4 25. 9 60. 449. 0 l9. 3 15. 0 74. 3 53. 8 26. 0 20. 2 20. 9 60. 2 40. 0 19. 3 20. 079. 3 50. 4 24. 4 25. 2 15. 9 60. 3 38. 0 19. 3 5. 4 62. 7 60. 6 30. 88. 6 36 9 59. 7 38. 0 19. 3 5. 4 62. 7 60. 6 30. 8 8. 6 35. 8 59. 7 38.0 19. 3 5. 4 62. 7 60. 6 30. 8 8. 6 34. 9 62. 6 36. 0 19. 3 5. 4 60. 759. 3 31. 8 8. 9 34. 9 59. 2 34. 0 19. 3 7. 4 60. 7 56. 0 31. 8 12. 234. 9 59. 9 42. 0 19. 3 5. 0 66. 3 63. 3 29. 2 7. 5 28. 9 60. 6 35. 0l9. 3 5. 0 59. 3 59. 0 32. 6 8. 4 35. 9 58. 8 36. 4 19. 3 7. 4 63. 1 57.7 39. 6 11. 7 34. 9 59. 7 34. 0 19. 3 7. 4 60. 7 56. 0 31. 8 12. 2 34. 959. 1 38. 0 19. 3 5. 4 62. 7 60. 6 30. 8 8. 6 34. 9 60. 2 40. 0 17. 3 5.4 62. 7 63. 8 27. 6 8. 6 34 9 60. 0 39. 9 13.2 7. 8 69. 9 65. 0 22. 913. 9 20. 0 56. 4 35. 7 21. 0 5. 8 62. 5 57. 1 33. 6 9. 3 36. 0 60. 1

Table 4 indicates examples for the melting of further optical crownglasses which are intended to demonstrate Welght: Percent thatpractically the entire range of the so-called heavy B 0 34-44 crownglasses may be attained with starting mixtures SiO 13-21 in accordancewith the present invention. A1 0 5-10 TABLE 4.IN PERCENT OF WEIGHT PER100% B 0 S102 A1203 21 B 0 S A1203 03.0 SrO B210 22 Lagog Z1O2 L120 N32011., V

61. 3 22. 5 83. 8 73. 2 26. 8 9. 1 9. 1 60, 5 56. 2 29. 6 76. 8 73. 226. 8 l6. 7 16. 7 60, 4 51. 8 19. 1 79. 9 73. 2 26. 8 23. 1 23. 1 60, 248. 1 17. 7 65. 8 73. 2 26. 8 28. 6 28. 6 59, 2 51. 8 19. 1 79. 9 73. 226 8 23. 1 23. 1 59, 5 48. 8 19. 1 67. 9 71. 9 28. 1 23. 1 23. 1 9. 9.59, 0 51. 8 19. 1 79. 9 73. 2 26. 8 29. 1 29. 1 9. 9 59. 6 51. 8 16. 167. 9 76. 3 23. 7 23. 1 23. 1 9. 9 59, G 48. 8 19. 1 67. 9 71. 9 28. 120. 1 20. 1 12. 9 58, 9 45. 8 19. 1 64. 9 79. 1 29. 9 29. 1 29. 1 15. 958, 45. 8 16. 1 61.9 74. 9 26. 9 29. 1 3. O 23. 1 15. 9 57, 9 45. 8 13.1 58. 9 77. 7 22. 3 29. 1 6. 9 26. 1 15. 0 58. 9 45. 8 5. O 19. 1 69. 965. 5 27. 3 15. 1 a. 9 29. 1 15. 9 58, 5 45. 8 19. 9 l9. 1 74. 9 61. 125. 5 19. 1 10. 9 20. 1 15. 9 58, 6 45. 8 16. 1 61. 9 74. 9 26. O 29. 129. 1 15. O 57, 1 45. 8 H 13. 1 58. 9 77. 7 22. 3 29. 1 29. 1 15. 9 55,8

The attached drawing illustrates the three-component the totalconcentration of these oxides in the mixture diagram of boric acid,silicic acid and aluminum oxide being from 55 to 75 Wt. percent, and

and locates a number of the examples of the tables Weight, percentthereon. The examples in the tables are identified by their CaO 25-37melt numbers. BaO 0-5 Obviously, many modifications and variations ofthe invention as hereinbefore set forth may be made without departingfrom the essence and scope thereof, and only the total concentration ofthese oxides in the mixture being from 25 to 40 wt. percent, and

such limitations should be applied as are indicated. La 0 Weightperceilt The invention claimed is: Li 3 1. Optical crown glass meltedfrom a mixture essen- 2 i u Consisting f 3. Optical crown glass meltedfrom a mixture essen Weighg t tially consisting of Weight, percent B 043.6 Si0 3.0 A1 0 9.9 the total concentration of these oxides in themixture C210 23.0 being from 55 to 62 wt. percent,

Weight, percent CaO 20-25 BaO 0-3 ZnO and/or CdO 0-10 4. Optical crownglass melted from a mixture conthe total concentration of these oxidesin the mixture Slstmg essennany of being from 23 to 35 wt. percent, andB 0 Weight gg Weight, percent 2 3 La O 14-16 ,-g Z102 Tazofi 0-5 La O1.0 2. Optical crown glass melted from a mixture eSSBH- L120 tiallyconsisting of (References 011 following page) References Ci'ei 255,9147/1948 Switzerland. UNITED STATES PATENTS 147,301 10/1962 2,466,5104/1949 Sun @1311 10647 PELEW M1 1 1cC/1P,T1IY, Primary Examiner2,996,392 8/1961 Bromer et a1. 106-47 3,248,238 4/1966 Faulstich 10654 5C1. FOREIGN PATEIITS 196-47 3,711,966 8/1962 Japan

